Cardiac resynchronization therapy (CRT) has been proven to be a good method to help patients with congested heart failure and bundle branch block. The optimal ventricular stimulation delay (VV-delay) is often selected by use of echocardiography or invasive LV dP/dt (max) measurements.
When using echocardiography, lateral movements of the interventricular septum indicate a suboptimal VV-delay. When the biventricular stimulation is performed with an optimal VV-delay, the septal movements laterally are minimized. Thus, if the propagation times from the right and left ventricles to the AV node in the septum is different, this can be compensated by a programmed VV-delay that ensures simultaneous arrival of the action potential to the septum.
Measuring left ventricular pressure gradient is an invasive procedure that only can be performed at a clinic. When septal movements are minimized the LV contractions are the most efficient which gives the highest dP/dt(max).
Neither echocardiography nor invasive pressure measurements can be performed outside clinic, which makes it difficult to continuously optimize the VV-delay in patients treated with cardiac resynchronization therapy (CRT).
The optimal VV-delay used for CRT will be changing over time due to remodelling and disease progression. Continuous optimization would therefore improve the cardiac function in long term and speed up the reverse remodelling process after start of therapy. The response to CRT would also be beneficial as the optimal setting always would be programmed in the device.
Thus, efforts have been made within the art to provide solutions for out-of-clinic methods and systems for continuous optimization of VV-delay and/or atrio-ventricular pacing delays (e.g. AV-delay or PV-delay).
St. Jude Medical's QuickOpt™ Timing Cycle Optimization is an algorithm that provides IEGM (Intracardiac Electrogram) based AV (Atrial-Ventricular) timing optimization in CRT and ICD (Implantable Cardioverter-Defibrillator) systems and VV (Ventricular-Ventricular) timing optimization in CRT devices in a simple and swift way. QuickOpt™ Timing Cycle Optimization is based on the hypothesis that the point of time for the closure of the Mitral valve can be estimated by measuring the interatrial conduction time (P-wave duration), that the onset of isovolumetric contraction can be measured using the peak of the R-wave and that interventricular conduction delays can be measured by evaluating simultaneous RV (Right Ventricular) and LV (Left Ventricular) IEGMs and measuring the time between the peaks of the R-waves. The goal is to characterize interatrial conduction patterns so that preload is maximized and ventricular pacing does not occur until after full closure of the mitral valve and to characterize intrinsic and paced interventricular conduction patterns so that pacing stimuli and the resultant LV and RV conduction (paced wave fronts) meet at the ventricular septum. Accordingly, QuickOpt™ Timing Cycle Optimization electrically characterizes the conduction properties of the heart to calculate optimal AV delay, PV delay (the time interval between a sensed atrial event and the ventricular impulse) and VV delay. QuickOpt™ Timing Cycle Optimization has been clinically proven to correlate with the more time-consuming echo-based methods and may be used for patients carrying CRT and dual-chamber devices at implant or follow up. QuickOpt™ Timing Cycle Optimization is an appealing optimization method since it does not require systematic measurements of a number of different AV and VV delays, which makes it very fast and simple. There are other IEGM based optimization methods among which QuickOpt™ Timing Cycle Optimization is one such method.
U.S. Pat. Appl. 2010/0145405 to Min et al., entitled “Systems and methods for controlling ventricular pacing in patients with long inter-atrial conduction delays”, presents a solution using QuickOpt™. In particular, atrio-ventricular conduction delays are measured and used for determining the pacing regime.
In U.S. Pat. Appl. 2010/0256701 to Muller, entitled “Determining site-to-site pacing delay for multi-site anti-tachycardia pacing”, a solution where interventricular delays are determined for use in anti-tachycardia pacing is disclosed. A left to right directional conduction time is determined, for example, an LV lateral wall to RV apex time, by delivering energy to a LV lateral wall site, by sensing the delivered energy at a RV apex site and by measuring the elapsed time. The RV apex to LV lateral wall time is thereafter determined. A pacing regime is determined based on an offset between these two time intervals.
In U.S. Pat. Appl. 2011/0022111 to Min, entitled “Systems and methods for optimizing ventricular pacing delays during atrial fibrillation”, methods and devices for optimizing interventricular (VV) pacing delays during AF (Atrial Fibrillation) are disclosed. A test to detect an intrinsic interventricular conduction delay for determining an optimal VV delay is performed. The test is initiated upon detection of AF based on high atrial rate. More specifically, separate RV pace and LV pace tests are performed to determine interventricular delays for left and right side (i.e. left to right conduction delay and vice versa). A RV test can be performed by first detecting RR intervals between RV QRS complexes on the RV channel. Then, RV pacing intervals are set to a period shorter than the detected RR intervals (e.g. 95% to 98% of the detected RR interval) to secure that the resulting LV QRS will arise via interventricular conduction and not via AV conduction from the atria. Right to left conduction delay is determined based on time delays between sequences of RV pacing pulses and respective detected resulting LV QRS's. For example, an average right to left conduction delay can be determined by averaging a set of such time delays. A similar procedure is performed to determine the corresponding time delay from left to right.
However, there is still a need within the art of improved systems and methods for continuous and automatic optimization of VV-delays of an implanted cardiac stimulator such as a pacemaker.